Teenagers are rarely taught the reason why they can't consent to sex with adults.
And that's because teaching them that would completely unravel our coercion-based society.
It can be difficult to explain in detail the exact reason and all the specifics in a way that they will understand. But the simplest way to phrase it is that in some cases, even when someone agrees to something and even when they appear enthusiastic about it, there's too much of a power imbalance that it's no different than forcing them. Also, having power and being abusive doesn't require a conscious expectation to be obeyed.
Imagine a world in which every teenager understood that and was easily able to call out anyone who tried to convince them otherwise.
They'd know that there's no such thing as an employee consenting to working for a poverty wage, working in unsafe conditions, working long hours, or working without taking breaks. They'd know that there's no such thing as consenting to paying a bank overdraft fee. They'd know that there's no such thing as consenting to student loan debt. They'd know that there's no such thing as consenting to medical bills. They'd know that there's no such thing as consenting to generating profit for banks or landlords in order to have a place to live and being evicted or foreclosed when you lose your source of income. They'd know that there's no such thing as consenting to a police search. They'd know that there's no such thing as a child who's okay with their parents spanking them. They'd know that being dependent on someone does not mean that you can never criticize them. They'd know that if it's considered abusive to simply play along when someone obeys, then it has to be much more abusive to actively expect to be obeyed, which many adults do to them.
And people who benefit from a society based on coercion masquerading as freedom wouldn't like that.
So instead, teenagers are taught something dismissive. They're taught that what they want doesn't matter. They're taught that they're too young to know what love is. They're taught "it's the law". They're taught things that are insulting to their intelligence, which they'll naturally rebel against.
